Heating pads are commonly used by individuals to provide controlled and localized heating to particular body parts or areas. The heating pads may be incorporated into an article of clothing, such as a glove, or may be provided as a stand alone article to be placed on an area which is desired to be heated. Heating pads typically include a heating element, such as a large resistive element, which is heated by the application of power. Heating pads also include a thermostat or other temperature control mechanism which allows a user to vary and control the amount of heat provided by the heating pad.
Heating pad temperature control may be achieved by controlling the amount of power delivered to the heating element within the heating pad. The amount of power is in turn controlled by altering either the amount of continuous power applied to the heating element, or intermittently applying power to thereby alter the amount of time during which power is applied to the heating element. This latter approach to temperature control is often referred to as “duty cycle” control, since it is the amount of on-time and off-time of the applied power that is being controlled.
Conventional heating pad controllers typically include a thermostat for sensing the heating pad temperature and turning off power to the heating element once the heating pad has reached a desired temperature. An additional “tickler” heater in thermal contact with the thermostat is selectively turned on to accelerate the turn-off of the thermostat, thus, shortening the on-time of the heating element and maintaining the heating element at a lower overall temperature. When a desired temperature setting is activated by a user controlled switch, current is supplied to a “tickler” heater. The added heat generated by the tickler heater in conjunction with the heat generated by the heating element causes the thermostat to reach its turn-off temperature sooner than it would without the application of the additional “tickler” heater. When the thermostat turns off, all power to the heating element and the tickler heater is also turned off. This results in a lower heating pad temperature setting since the heater on-time is shortened due to the quick turn-off of the thermostat.
FIG. 1 shows a conventional heating pad controller which includes a “tickler” heater H1 for regulating the different heat settings. As shown in FIG. 1, thermostats T1 and T2 sense the temperature of the heating pad which is heated by heater H3
Additionally, thermostat T1 is in thermal contact with heater H1, a small “tickler” heater. User control is provided via switch S, which is a four position switch. In the high switch setting, contacts S3 and S4 are connected together; in the medium setting, contacts S3 and S4 are connected together and contacts S2 and S5 are connected together; in the low setting, contacts S2 and S5 are connected together; while in the off setting, contacts S1 and S6 are connected together. In the low setting, all the current flows through heater H1, which in turn heats thermostat T1 causing it to prematurely turn off, thus maintaining primary heater H3 at a lower overall temperature. The current also flows through heater H3 causing it to warm up. In the medium setting, some of the current is diverted through heater or resistor H2, which is more thermally isolated from thermostats T1 and T2 than heater H1. This results in heater H1 applying less heat to thermostat T1 such that thermostat T1 remains on for a relatively longer period of time, thus keeping heater H3 at a medium temperature. In the high setting, no current flows through heater H1, and thus there is no additional or accelerated heating of thermostat T1. This results in heater H3 being maintained at the highest temperature level limited only by thermostats T1 and T2 which are typically required in order to meet the prevailing safety codes for such devices.